1. Field of the Invention
The present invention relates to a sewing device for sewing a cloth to be sewn (referred to as a sewn product hereinafter) at both sides thereof concurrently.
2. Prior Art
In case of sewing a mask cloth A made of gauze as illustrated in FIG. 10, conventionally the folded mask cloth A is sewn by a sewing machine alternately along a line apart from each side thereof by a given distance ML to form a stitch line FT in each side portion thereof. Moreover, back tack stitches BT are formed at the start and end of sewing to prevent the stitch lines FT from coming loose.
As described above, a conventional mask sewing device employs a normal sewing machine for alternately sewing each side thereof. As a result, efficiently sewing a mask of high quality which has uniform stitch lines symmetrical to each other on both sides thereof requires a skilled operation, causing a bottleneck in rationalizing the sewing processes in a sewing factory.
Moreover, generally in a sewing factory, sewn products each having a given dimension such as mask cloths are sewn one after another by a continuously operating sewing machine and thereafter an operator cuts off the portions of the needle and bobbin threads which connect the sewn products to one another.
When an operator cuts off the connecting portions, the length of the connecting portions is desirable to be on the order of several millimeters in order to cut off the same in one cutting operation. When the connecting portions are too long, additional operation is needed to cut off again the connecting portions remaining to the mask cloths, and when they are too short, the mask cloths are liable to be damaged by mistake in cutting.